The purification process (the pumping process) brought about by the vertical pumping device comprises a vacuum system (underpressure system) which creates an underpressure in the fluorescent tube body and a targeted particle flow with particles to be removed from the fluorescent tube body. This particle flow in the fluorescent tube body stops when degassing of substances has ceased. Sometimes, the particle flow may even reverse.
In order to solve this problem, a technique has been developed which supplies substances creating a new particle flow. This technique employs liquid mercury, which is applied in the interior of the fluorescent tube body at the lower part of the fluorescent tube body. The mercury gasifies with great expansion. The gasified mercury also has the ability to bind contaminants. At the expansion, the mercury thus binds the contaminants and conveys them out of the fluorescent tube body in the additional particle flow obtained. The liquid mercury, provided in order to create the additional particle flow, is dosed at the pumping process in a first position where gasification has ceased and pumping out of particles is most desirable. The dosing is done by flow throttling. When the lamp then reaches the end of the vertical pumping device with ensuing final filling of the lamp gas, an additional amount of mercury will be dosed into the fluorescent tube body to provide the lamp gas for the operation of the fluorescent tube. Earlier on, vertical pumping devices were thus filled with liquid mercury, which worked production-technically, but which at the same time entailed a ten percent loss of mercury.
The document JP 2000208050 shows a device for distributing bound mercury in pellet form. An electromagnet is arranged to lift a valve when the intended pellets are supplied. The aim with the device is to prevent involuntary supply of pellets into the fluorescent tube body because of device vibrations.